1. Field of the Invention
This invention relates to the field of radio frequency identification (RFID) tags and labels.
2. Description of the Related Art
RFID tags and labels have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. RFID tags and labels are widely used to associate an object with an identification code. For example, RFID tags are used in conjunction with security-locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,292, all of which this application incorporates by reference.
RFID tags and labels include active tags, which include a power source, and passive tags and labels, which do not. In the case of passive tags, in order to retrieve the information from the chip, a “base station” or “reader” sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The “reader” receives and decodes the information from the RFID tag. In general, RFID tags can retain and transmit enough information to uniquely identify individuals, packages, inventory and the like. RFID tags and labels also can be characterized as to those to which information is written only once (although the information may be read repeatedly), and those to which information may be written during use. For example, RFID tags may store environmental data (that may be detected by an associated sensor), logistical histories, state data, etc.
Still other RFID devices and methods for manufacturing RFID labels are disclosed in U.S. Patent Application Publication No. US2001/0053675 by Plettner, which is incorporated herein by reference in its entirety. The devices include a transponder comprising a chip having contact pads and at least two coupling elements, which are conductively connected with the contact pads. The coupling elements are touch-free relative to each other and formed in a self-supported as well as a free-standing way and are essentially extended parallel to the chip plane. The total mounting height of the transponder corresponds essentially to the mounting height of the chip. The size and geometry of the coupling elements are adapted for acting as a dipole antenna or in conjunction with an evaluation unit as a plate capacitor. Typically, the transponders are produced at the wafer level. The coupling elements can be contacted with the contact pads of the chip directly at the wafer level, i.e., before the chips are extracted from the grouping given by the wafer.
In many applications, it is desirable to reduce the size of the electronics as small as possible. In order to interconnect very small chips with antennas in RFID inlets, it is known to use a structure variously called “interposers”, “straps”, and “carriers” to facilitate inlay manufacture. Interposers include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling to the antennas. These pads provide a larger effective electrical contact area than ICs precisely aligned for direct placement without an interposer. The larger area reduces the accuracy required for placement of ICs during manufacture while still providing effective electrical connection. IC placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID interposer or strap structures, typically using a flexible substrate that carries the interposer's contact pads or leads.
One type of prior art RFID inlet manufacture using interposers is disclosed in European Patent Application EP 1039543 A2 to Morgan Adhesives Company (“Morgan”). This patent application discloses a method of mounting an integrated circuit chip (IC) using an interposer connected across a gap between two thin conductive film sections of a conductive film antenna. The interposer comprises a thin substrate having two printed conductive ink pads. This method is said to be suitable for mass production of radio frequency identification tags (RFIDs) by mounting ICs on interposers that are then physically and electrically connected to the antenna sections using a pressure sensitive conductive adhesive. The pressure sensitive conductive adhesive provides a direct electrical connection between the interposer contact pads and the antenna sections.
Another type of prior art RFID inlet manufacture using interposers is based on a technique for manufacturing microelectronic elements as small electronic blocks, associated with Alien Technology Corporation (“Alien”) of Morgan Hill California. Alien has developed techniques to manufacture small electronic blocks, which it calls “NanoBlocks”, and then deposit the small electronic blocks into recesses on an underlying substrate. To receive the small electronic blocks, a planar substrate 200 (FIG. 1) is embossed with numerous receptor wells 210. The receptor wells 210 are typically formed in a pattern on the substrate. For instance, in FIG. 1 the receptor wells 210 form a simple matrix pattern that may extend over only a predefined portion of the substrate, or may extend across substantially the entire width and length of the substrate, as desired. Alien has a number of patents on its technique, including U.S. Pat. Nos. 5,783,856; 5,824,186; 5,904,545; 5,545,291; 6,274,508; and 6,281,038, all of which the present application incorporates by reference. Further information can be found in Alien's Patent Cooperation Treaty publications, including WO 00/49421; WO 00/49658; WO 00/55915; WO 00/55916; WO 00/46854 and WO 01/33621, all of which this application incorporates by reference in their entireties.
Alien's NanoBlock technology is adapted to interposer manufacture for producing RFID inlets in U.S. Pat. No. 6,606,247. A carrier substrate or interposer is coupled to an IC that is recessed below a surface of the interposer. The interposer further includes first and second carrier connection pads that interconnect with the IC using metal connectors. A planar antenna substrate carries first antenna sections with respective first and second receiving connection pads. The carrier substrate is coupled to the antenna substrate using the carrier connection pads and receiving connection pads. In contrast to the interposer of Morgan's European publication EP 1039543 A2 in which the IC is mounted above the interposer contact pads at the surface of the interposer substrate, in U.S. Pat. No. 6,606,247 the chips are retained in recesses in the interposer substrate, and the carrier connection pads are formed above the IC. However, both EP 1 039 543 A2 and U.S. Pat. No. 6,606,247 share the feature that the interposer or strap pads are directly electrically connected to the antenna sections using conductive adhesive.
Another problem to be solved in producing inlays using interposers is the reliable high speed mechanical and electrical coupling of the interposers (and interposer leads) to antennas. The present invention, in contrast to Morgan's EP 1 039 543 A2 and Alien's U.S. Pat. No. 6,606,247, uses a non-conductive adhesive to mechanically couple the interposer leads to the antenna sections. Non-conductive adhesives can facilitate high speed production in comparison to conductive adhesives, due to reduction of cure time requirements and production cycle times. However, since the adhesive is not electrically conductive, another mechanism (besides electrical conduction by the adhesive) must be provided to electrically couple the interposer leads to the antenna sections.
From the foregoing it will be seen that room exists for improvements in RFID tags and methods of assembling such tags.